Results of behavioral and audiological tests with humans imply that ability to understand speech and other complex signals (particularly in a noisy listening situation) suffers deterioration from noise insult in excess of what could be inferred from pure tone thresholds mealsured in the quiet. These findings suggest that a complex interaction occurs between the various levels of the auditory nervoud system and that functionally different receptors of the auditory end organ play a vital role in "sharpening" the sensory process. The objective of this study is to use the rapid signal analysis ability of minicomputers to determine the auditory response to speech and speech-like signals including pseudorandom noise under normal conditions and conditions of auditory fatigue. Auditory fatigue and recovery process of single nerve fibers to speech and speech-like stimuli will be studied. The requirements in high speed data throughput for nearly absolute phase matching of input acoustical and output physiological signals, and for accurately processing neural pulse trains necessitated the design and building of several unique complex peripheral devices.